A structural spacing core material, popularly known as honeycomb, is often sandwiched between a pair of exterior panels to provide a lightweight, high strength, rigid panel which has many uses of which building material, building partitions, ceilings and aircraft cabin interiors are but a few examples. These panels, in this form, have very little sound absorption capability. To increase sound absorption, the cells were filled with an acoustical absorbing media such as a compressible fiberous batting or a fiberglass wool. Normally, this was a hand-operation, such as by rolling, punching or hand-stuffing. It is important in filling the honeycomb cells with the sound absorbing material that the fibers be fully contained within the cells without extending across the edge surfaces that are to be bonded to the outer panels.